The Explorer: Resource Leaks, Part One - InformationWeek

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1/7/2004
02:28 PM
Fred Langa
Fred Langa
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The Explorer: Resource Leaks, Part One

Crashes can sometimes be traced to sloppy programs that "leak" memory.

The Mythical "System Resources"
To begin with, there's no single thing called "System Resources." It actually means different things depending on how it's used. Most generally, it refers to all the components of your PC that let it do what it does.

But the "System Resources" that John's letter mentioned are two very specific memory areas inside Windows: User Resources and GDI (Graphics Device Interface ) Resources. You can think of these areas as scratchpads -- actually, internal tables and pointers -- that Windows uses to keep track of running applications.

The User area contains information about all the apps and windows currently running, including dialog boxes, the controls in dialog boxes, and so on. Every DLL, in fact, your apps use gets its own data area in the User section.

Loosely speaking, the more things you ask your computer to do at once, the more heavily used your User area becomes.

The GDI area keeps track of the things Windows uses to draw what you see on screen: there are things called pens, brushes, fonts, bitmaps, regions, and palettes, for example. Roughly speaking, the more graphical objects you have on-screen -- windows, icons, wallpapers, etc. -- the more heavily used your GDI area becomes.

Both resource areas are of a fixed size regardless of how much RAM you have -- and that's the problem. If you run too many things at once or have too many graphical objects displayed at once, you can deplete the User or GDI area. When that happens, you get the error messages mentioned earlier, or weird behavior or a crash.

The Good News
With properly-coded applications (that's a major caveat), it's actually fairly hard to run out of System Resources. I just tried an experiment, for example, on my main Win98SE system here: I opened (as normal windows) Internet Explorer, my Office 2000 suite (Access, Outlook, Word, Excel, PowerPoint and FrontPage), Lotus Organizer, an MS-DOS window, and Eudora (a notorious resource hog), plus a couple of small "tray" apps I always have running. It's hard to imagine a single person needing to run much more than that at the same time, but Windows could have done lots more -- I still had 28 percent system resources free!

(And by the way: You can thank Windows Magazine -- the predecessor of WinMag.com -- for this ability of Windows to handle so many apps with ease. You see, during the early beta testing of what was to become the original Windows 95, the folks at WinMag discovered that the new OS retained the tiny, inadequate System Resource areas of the old Windows 3.1. WinMag complained to Microsoft, in print, and Microsoft responded by making Windows 95's System Resource areas far larger than they'd planned to. It's a little-known fact, but literally every person who has ever used any version of Windows 9x has benefited from the aggressive testing and reporting of Windows Magazine!)

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